Polish mathematical physicist Roman Stanisław Ingarden publishes a seminal paper entitled "Quantum Information Theory" in Reports on Mathematical Physics, vol. 10, 43–72, 1976. (The paper was submitted in 1975.) It is one of the first attempts at creating a quantum information theory, showing that Shannon information theory cannot directly be generalized to the quantum case, but rather that it is possible to construct a quantum information theory, which is a generalization of Shannon's theory, within the formalism of a generalized quantum mechanics of open systems and a generalized concept of observables (the so-called semi-observables).

1980s

Richard Feynman observes in his talk at the First Conference on the Physics of Computation, held at MIT in May, that it appeared to be impossible in general to simulate an evolution of a quantum system on a classical computer in an efficient way. He proposes a basic model for a quantum computer that would be capable of such simulations[4]

Paul Benioff gives talk at the same conference with the title "Quantum mechanical Hamiltonian models of discrete processes that erase their own histories: application to Turing machines".

Bikas K. Chakrabarti & collaborators from Saha Institute of Nuclear Physics, Kolkata, proposes the idea that quantum fluctuations could help explore rough energy landscapes by escaping from local minima of glassy stems having tall but thin barriers by tunneling (instead of climbing over using thermal excitations), suggesting the effectiveness of quantum annealing over classical simulated annealing.

Peter Shor, at AT&T's Bell Labs in New Jersey, discovers an important algorithm. It allows a quantum computer to factor large integers quickly. It solves both the factoring problem and the discrete log problem. Shor's algorithm can theoretically break many of the cryptosystems in use today. Its invention sparked a tremendous interest in quantum computers.

First United States Government workshop on quantum computing is organized by NIST in Gaithersburg, Maryland, in autumn.

Christopher Monroe and David Wineland at NIST (Boulder, Colorado) experimentally realize the first quantum logic gate – the controlled-NOT gate – with trapped ions, following the Cirac-Zoller proposal.[9]

1996

Lov Grover, at Bell Labs, invents the quantum database search algorithm. The quadratic speedup is not as dramatic as the speedup for factoring, discrete logs, or physics simulations. However, the algorithm can be applied to a much wider variety of problems. Any problem that has to be solved by random, brute-force search, can take advantage of this quadratic speedup (in the number of search queries).

The United States Government, particularly in a joint partnership of the Army Research Office (now part of the Army Research Laboratory) and the National Security Agency, issues the first public call for research proposals in quantum information processing.

David P. DiVincenzo, from IBM, proposes a list of minimal requirements for creating a quantum computer.[10]

Bruce Kane proposes a silicon based nuclear spin quantum computer, using nuclear spins of individual phosphorus atoms in silicon as the qubits and donor electrons to mediate the coupling between qubits.[14]

Daniel Gottesman and Emanuel Knill independently prove that a certain subclass of quantum computations can be efficiently emulated with classical resources (Gottesman–Knill theorem).[15]

1999

Samuel L. Braunstein and collaborators show that none of the bulk NMR experiments performed to date contained any entanglement, the quantum states being too strongly mixed. This is seen as evidence that NMR computers would likely not yield a benefit over classical computers. It remains an open question, however, whether entanglement is necessary for quantum computational speedup.[16]

2000s

2000

Arun K. Pati and Samuel L. Braunstein proved the quantum no-deleting theorem. This is dual to the no-cloning theorem which shows that one cannot delete a copy of an unknown qubit. Together with the stronger no-cloning theorem, the no-deleting theorem has important implication, i.e., quantum information can neither be created nor be destroyed.

Noah Linden and Sandu Popescu proved that the presence of entanglement is a necessary condition for a large class of quantum protocols. This, coupled with Braunstein's result (see 1999 above), called the validity of NMR quantum computation into question.[17]

Emanuel Knill, Raymond Laflamme, and Gerard Milburn show that optical quantum computing is possible with single photon sources, linear optical elements, and single photon detectors, launching the field of linear optical quantum computing.

First five-photon entanglement demonstrated by Jian-Wei Pan's group at the University of Science and Technology of China, the minimal number of qubits required for universal quantum error correction.[22]

2005

Two teams of physicists measured the capacitance of a Josephson junction for the first time. The methods could be used to measure the state of quantum bits in a quantum computer without disturbing the state.[23]

In December, the first quantum byte, or qubyte, is announced to have been created by scientists at the Institute of Quantum Optics and Quantum Information at the University of Innsbruck in Austria.[24]

2006

Researchers from the University of Illinois at Urbana–Champaign use the Zeno Effect, repeatedly measuring the properties of a photon to gradually change it without actually allowing the photon to reach the program, to search a database without actually "running" the quantum computer.[26]

Vlatko Vedral of the University of Leeds and colleagues at the universities of Porto and Vienna found that the photons in ordinary laser light can be quantum mechanically entangled with the vibrations of a macroscopic mirror.[27]

Quantum computer, along with quantum superposition and entanglement, emulated by a classical analog computer, with the result that the fully classical system behaves like a true quantum computer. [182]

2016

Google, using an array of 9 superconducting qubits developed by the Martinis group and UCSB, simulates a hydrogen molecule.[183]

2017

D-Wave Systems Inc. announces general commercial availability of the D-Wave 2000Q quantum annealer, which it claims has 2000 qubits.[184]

Scientists build a microchip that generates two entangled qudits each with 10 states, for 100 dimensions total.[188]

Microsoft reveals an unnamed quantum programming language, integrated with Visual Studio. Programs can be executed locally on a 32-qubit simulator, or a 40-qubit simulator on Azure.[189]

Intel confirms development of a 17-qubit superconducting test chip.[190]

IBM reveals a working 50-qubit quantum computer that can maintain its quantum state for 90 microseconds.[191]

2018

MIT scientists report the discovery of a new triple-photon form of light.[192][193]

Oxford researchers successfully used a trapped-ion technique where they place two charged atoms in a state of quantum entanglement, to speed up logic gates by a factor of 20 to 60 times as compared with the previous best gates, translated to 1.6 microseconds long, with 99.8% precision.[194]